Various types of electrical insulators have been constructed in the past to support heater coils within an electric heater assembly suitable for use in many applications and in particular for use in an electrically heated clothes dryer. In such heater assemblies, the heater coils are mounted directly to supporting arms of the insulator which in turn is mounted to a heater assembly support.
One example of an insulator is disclosed in U.S. Pat. Nos. 4,531,017issued Jul. 23, 1985 and 4,675,511 issued Jun. 23, 1987, both by Jimmy Sherrill. These patents disclose an electrical insulator having two support arms spaced apart and that extend from a base. The arms have inclined outer guide surfaces that provide the shape of an arrowhead for the insulator. The outside inclined guide surfaces have inwardly directed notches. The arrowhead insulator also has a central slot between the arms with a notch at the bottom of the slot adjacent the base and horizontally aligned with the two side notches. The insulator supports the coil at three consecutive coil convolutions. An important feature of this insulator is that the upper ends of the guide surfaces are smaller than the distance between the outer convolutions of the coil and the distance between the bottoms of the notches in the sidewalls. This allows the coil to be firmly placed into the elongated slot and adjacent coil convolutions to be spread over the inclined outer guide surfaces and sprung back into place in the inwardly directed side notches. While this arrowhead design provides a support for a heater coil that may be readily mounted to the insulator, there is a problem associated with the coil flexing relative to the insulator during operation. This occurs due to the cyclic heating and cooling of the heater coil during operation. When the heater coil is heated it has a tendency to expand. This expansion places stresses on the coil at the insulator. Consequently, the heater coil has a tendency to flex upwardly or outwardly between the insulators causing the adjacent convolutions of the heater coil diametrically opposed to those convolutions supported by the insulator to flex toward each other during a heating cycle. During repeated heating cycles the coils have a tendency to be mechanically fatigued and break at locations adjacent the insulator. Also, the heater coil has a tendency to expand touching adjacent metallic parts and then breaking.
Another similar insulator is shown in U.S. Pat. No. 4,628,189which issued Dec.9, 1986 to Michael Danko. The electrical resistance insulator is similar to that disclosed in the aforementioned U.S. Pat. Nos. 4,531,017 and 4,675,511, however the slope or arcuate angle of the side guide surface relative to the side notch is greater than that disclosed in the aforementioned U.S. patents. Further, the central slot is tapered. Danko discloses that preferably the distance between the tips of the arrowhead and the ends of the sidewall notches is somewhat greater than half the diameter of the coil. The central slot is located to be slightly off center from the horizontal direction of the convolutions of the coil held in the side slots. This creates a reverse bending in the coil which counteracts any bowing in the heater coil outwardly during a heating cycle. However, the heater coil is still supported at three locations relative to the insulator on one diametrical side of the coil which allows stresses to be placed on the outer convolutions of the heating coil adjacent the insulator causing them to flex and provide a localized area on the coil that is subject to fatigue and failure.
There is a need to provide an electrical resistant insulator that supports a helically wound heater coil and prevents the heater coil from moving at the convolutions of the heater coil diametrically opposed from the convolutions of the heater coil normally supported by the electrical insulator while still permittng for simple assembly of the is heater coil onto the insulator.